Viscous-fluid-containing inertia dampers are employed to absorb energy from a moving system, and often are employed with stepper motors and similar devices. A stepper motor transforms electrical energy, such as electrical pulses, into mechanical movement through the specific angular movement of the motor output shaft for each amount of electrical energy or electrical pulse received by the motor. Repetition of the electrical pulses and control by drive-motor circuity permit accurate movement and positioning of the output shaft, in comparison to conventional motors which have free-running shafts. The stepper motor includes a plurality of poles and a stator, and in operation, when the electrical energy is terminated, the stator tends to oscillate between poles before stopping completely. Thus, stepper motors are widely and usefully employed for rotational mechanical indexing a prescribed distance.
In order to inhibit oscillatory movement with stepper motors or other mechanical systems which tend to oscillate or develop resonance, viscous inertia dampers are used to absorb the rotation energy on stopping, rather than solely using the inherent function of a stepper motor to stop the stator between poles.
A typical viscous-fluid inertia damper has a housing and a cover, a heavy seismic mass within the housing, a viscous liquid, such as a silicone like Dow Corning DC #200 silicone, to absorb energy by providing a viscous shear force between the walls of the housing and the seismic mass, means to suspend the seismic mass in the housing, such as ball bearings supporting the seismic mass on a center post in the housing, and means adapted to be coupled to the output shaft of the stepper motor and to permit rotation of the seismic mass with the rotation of the shaft of the motor.
In operation, the energy of the rotating shaft of the stepper motor is rapidly dissipated by the viscous shear force of the damper.